Project Summary Adipose tissue is a central player in energy balance and glucose homeostasis, it is able to expand in the face of caloric overload in order to store energy safely, but it can become overloaded and dysfunctional, leading to systemic metabolic compromise in the form of insulin resistance and Type 2 diabetes. Transcription factors such as interferon regulatory factor 4 (IRF4) are key regulators of adipose tissue function, but there is much we still do not know about IRF4 regulation. We performed mass spectrometry for IRF4 binding partners in adipocytes, as well as ChIP-seq to generate a cistrome for IRF4 at the basal state, and found that IRF4 physically interacts with and may be negatively regulated by the closely related protein IRF8. We further found that IRF8 fat specific knockout animals show an opposite phenotype to IRF4 fat specific knockouts, further indicating the inverse roles of these proteins. In this application my objective is to definitively identify and characterize the IRF4:IRF8 interaction and its consequences in adipocytes. To do this I will characterize this physical interaction by studying the metabolic conditions under which IRF4 and IRF8 are likely to interact and assaying the functionality of point mutants that can no longer bind each other. I will further generate a cistrome for IRF8 binding in adipocytes and study how the cistromes of both IRF4 and IRF8 change under different metabolic stressors. Finally, I will investigate the dependence of the IRF8 phenotype on its negative regulation of IRF4 by breeding fat specific double knockout animals and metabolically phenotyping them. By studying the regulation of IRF4 in adipocytes, both by IRF8 and by metabolic stimuli, we can better understand and target pathways that can allow adipocytes to maintain metabolic homeostasis during obesity and thus prevent metabolic disease.